Overlay for printing



United States Patent U.S. Cl. 117-76 5 Claims ABSTRACT OF THE DISCLOSURE An overlay for printing includes a chalk relief layer consisting of chalk and a plastic binder which is not swellable in water. The chalk relief layer is applied to a smooth plastic supporting sheet. An intermediate layer consisting of a water swellable size may be disposed in between the chalk relief layer and the plastic supporting sheet.

This application is a continuation of US. patent application Ser. No. 441,374, file-d Mar. 19, 1965, now abandoned.

The present invention relates to an overly for book and illustration printing in connection with which a layer forming a relief which corresponds to the printing image after the printing and etching is applied to a supporting sheet.

Such sheets are today generally made in the form of so-called chalk overlays in connection with which there are applied to a supporting sheet of paper a number of layers which consist essentially of inorganic components, for instance calcium carbonate, kaolin and the like, and a binder, for instance size, which is attacked by an etching agent, particularly hypochlorite solution. An imprint of the desired printing image is produced on such a overlay. In this way, those points which are to be elevated are protected by the density of the printing ink applied from attack by the etching agent to a greater or lesser extent so that therefore etching takes place only at the points at which no printing ink has been applied. Such overlays give a gradation of relief of correct tonal value by which even small intermediate tonal values of the picture are produced. Furthermore, such overlays have excellent strength on printing. However, they have the disadvantage that the papers used as supporting sheet are not completely dimensionally stable so that a shrinkage of up to more than 1% occurs upon the etching process and drying.

In accordance with the invention, complete dimensional stability of the overlays can be obtained if the supporting sheet consists of a sheet of a macromolecular plastic or contains a plastic which is not swollen or merely reversibly swollen by the etching agent. Overlays produced with such supporting sheets no longer change during the etching process. The changes which can be noted in the case of the known sheets as a result of variations in relative humidity in the printing plant or upon storage also are without influence on these sheets.

In particular, sheets of polyester, polyvinyl chloride and polyvinylidene chloride or their copolymers can be used. However, polycarbonate, polyamide, polystyrene, polystyrene copolymers, cellulose acetates, pretreated polyolefins, Weather-proofed cellulose hydrate and the like can also be used as sheet material.

3,493,420 Patented Feb. 3, 1970 ICC One can, however, also use sheets which consist of a paper which is impregnated and possibly coated with an aldehyde resin which acts as cross-linking agent and a dispersion of a synthetic resin which does not swell in water, particularly a vinyl resin. The coherence of the paper texture and thus the dimensional stability is produced in this connection primarily by the addition of cross-linking agents, such as methylol urea, methylol melamine, phenol formaldehyde resins, in which connection bivalent aldehydes, such as glyoxal or dialdehyde starches, possibly in the presence of acid catalysts, such as oxalic acid, ammonium chloride, zinc chloride and the like, have proven suitable. These cross-linking agents by themselves exert an embrittling action in the concentrations necessary for the stabilizing of the dimensions. This embrittlement is now eliminated by the further plastic dispersions used. For this purpose, there can be used for instance plasticizer-free copolymers of vinylidene chloride with other polymerizable compounds, carboxylated dispersionswhich thus exert a cross-linking action between the polymer particles of plastic, fibers and sizing agent of butadiene-styrene, butadiene-acrylonitrile, acrylic-acidmodified vinylidene chloride emulsions or self-crosslinking nitrogen-containing polyacrylates. These plastic emulsions avoid furthermore any stresses which might still occur upon the drying of the wet paper. Furthermore, they increase the wet-strength of the paper since the fibers are surrounded by the hydrophobic synthetic resins.

Finally, papers of fully synthetic fibers, for instance having a base of polyamide, can be used.

The chalk relief layer can be applied in customary manner to this supporting sheet. In order to make certain that this layer which is of a thickness of 0.05 to 0.3 mm. withstands the shearing forces which occur upon the printing of the overlay with a viscous printing ink, and after the etching process, withstand the pressures acting thereon upon the printing of the run, one can, in accordance with the invention, particularly when using supporting sheets having smooth surfaces and therefore for instance plastic sheets, apply first of all directly to the supporting sheet at least one intermediate layer which contains the inorganic components forming the chalk relief layer together with a plastic binder which is not swellable in water, and possibly a size which is swellable in water and can be attacked by the etching agent. It is particularly advantageous to use at least two such intermediate layers, only the second of which contains the size which is attacked by the etching agent. Furthermore, in accordance with the invention, there can be added to one or more of these intermediate layers an organic coloring substance by which the end of the etching process is indicated to the printer.

By these intermediate layers there is assured a firm bonding of the chalk relief layers to the plastic supporting layer. There is produced a transition between the hydrophobic support sheet and the hydrophilic etching layer in which the inorganic components are bound with water-swellable size. On the one hand, the inorganic com-' ponents, the pigments, are bound to the hydrophobic base by the plastic binders which are not swellable in water while on the other hand there is thereby obtained a roughness which permits the application of the additional pigment layers and assures dependable adherence.

Such layers can also be used when it is desired not to produce overlays but rather for instance to make possible or improve the printability of plastic sheets, especially with regard to printing with ink customary in paper printing. The same applies with respect to writa'bility or the like.

If two intermediate layers are used, they can have the following composition- (1) First intermediate layer:

Parts China clay 70-100 Barium sulfate 10-20 Water 25-80 Vinyl isobutyl ether/methacrylate copolymer 15-50 'Defoaming agent 0.1-0.3 Wetting agent 0.l5-0.4 Organic coloring substance 0.2-0.6 (2) Second intermediate layer:

Parts China clay 60-80 Calcium carbonate 30-40 Water 30-60 Ammonia casein -30 Vinyl isobutyl ether/methacrylate copolymer -25 Defoaming agent 0.2-0.3 Wetting agent 0.1-0.3 Organic coloring substance 0.2-0.6

Instead of the above-indicated plastic binder, there can also be used in the above-indicated concentration carboxylated butadiene-styrene latices, plasticized chlorinecontaiuing vinyl copolymers, polyacrylates, polyvinylacetates or methylol compounds (5 to referred to the binder), hardened polyvinyl methyl ethers and polyvinyl isobutyl ethers.

These intermediate layers can be applied in a thickness of about 0.01 mm. to the supporting sheet. As sheet material for the said compositions, supporting sheets consisting in particular of rigid PVC or polyesters are suitable.

The layers required for the relief etching can be applied in any desired manner by multiple coating onto these intermediate layers. For example, there can be used the compositions which have been known for a long time in which calcium carbonate, kaolin, barium sulfate and satin white, as well as corresponding quantities of animal sizes and softening agents are used.

Etchable chalk relief coatings can be applied also to both sides of the overlay sheet in accordance with the invention, as is already known also in the case of the known chalk overlay sheets.

The overlay sheets in accordance with the invention dry very fast after the etching and there need not be applied any special measures for the drying as was the case in connection with the known overlay sheets. They can also be stored without special precautionary measures, since they are insensitive to atmospheric moisture.

Finally the overlay sheets in accordance with the invention need not have a rear coating applied to them as was necessary in part in the case of the known sheets since the etching agent also passed through the paper supporting sheet and attacked the chalk layer so that the hollowing out of said layers was feared. Such an action on the part of the etching agent through the supporting sheet is naturally no longer to be feared when the supporting sheet consists of a sheet of plastic.

What we claim is:

1. In an overlay for printing consisting of a supporting sheet, a chalk relief layer applied thereto, said chalk relief layer consisting essentially of calcium carbonate, china clay, kaolin, barium sulfate, or combinations thereof, and a water-swellable size, said'size being attackable by an etching agent, said chalk relief layer being adapted to permit the formation of a relief corresponding to a printed image, wherein the improvementcomprises said supporting sheet being formed entirely from .a substance taken from the class consisting of polyester, polyvinyl chloride, polyvinylidine chloride and copolymers thereof, polycarbonate, polyarnide, polystyrene, polystyrene copolymers, cellulose acetates, pre-treated polyolefins and weather-proofed cellulose hydrate, and the surface of said supporting sheet in contact with said chalk relief layer is smooth.

2. An overlay according to claim 1, including an intermediate layer disposed between said chalk relief layer and said supporting sheet, said intermediate layer comprising calcium carbonate, chinaclay, kaolin, barium sulfate, or combinations thereof, and a plastic binder which is not swellable in water.

3. An overlay according to claim 2, wherein said intermediate layer also contains a water-swellable size, said size being attackable by an etching agent.

4. An overlay according to claim 3, wherein said size is ammonia casein:

5. An overlay according to claim 2, including a secon intermediate layer disposed between said chalk relief layer and said supporting sheet, said second intermediate layer comprising calcium carbonate, china clay, kaolin, barium sulfate, or combinations thereof, and a water-swellable size which is attackableby an etching agent.

References Cited UNITED STATES PATENTS 892,166 6/1908 Lankes et al. l01-40l.3 1,324,038 12/1919 Dickhaut 101-4013 2,265,974 12/1941 Heinecke l0l-40l.3 2,680,682 6/ 1954 Dearing.

2,964,423 12/1960 Van Stappen 1l7-76 WILLIAM D. MARTIN, Primary Examiner R. HUSACK, Assistant Examiner US. Cl. X.R. 

